Paramyxoviruses are the major cause of respiratory disease in children. The long-term objective is to develop means to prevent respiratory disease caused by paramyxoviruses. To reach that objective, the proposed research will focus on structure-function relationships of the hemagglutinin-neuraminidase (HN) envelope glycoprotein of Newcastle disease virus (NDV), a prototypic paramyxovirus, in virus attachment, neuraminidase and fusion-promoting activity. The aims outline Dr. Portner's strategy to achieve his goals. Aim 1: Proposal: To establish a high resolution three-dimensional (3-D) structure of HN. Aim 2: Proposal: To determine directly the location and 3-D structure of the receptor binding, neuraminidase, and fusion promoting activities of HN. Dr. Portner's laboratory has crystallized the NDV HN protein by the hanging drop-vapor diffusion method. These crystals diffract X-rays at moderately high resolution (up to 2.6A) indicative that they will be suitable for determination of the HN 3-D structure. In Aim 1, the preparation of large amounts of larger crystals will be pursued with the prospect of increasing the resolution and to aid in obtaining and analyzing heavy metal derivatives essential to the solution of the HN structure. Aim 2 will determine directly the location and spacial arrangement of regions tentatively defined as the receptor binding and neuraminidase (NA) sites by analyzing the 3-D structure of HN complexed with sialic acid analogues. Supporting evidence will come from mutational analysis of cell binding and NA activities expressed from cDNAs that contain site-directed mutations in the proposed NA and cell binding sites, and isolation and sequence analysis of receptor specificity mutations and escape mutants. Mutational analysis and knowledge of the 3-D structure should provide an assessment of the location and structure of the fusion promoting domain associated with the globular head region of HN, thus providing additional targets for drug intervention.